http://www.direct.gov.uk/en/disabledpeo ... g_10034898
This link explains the funding for support at university. To access it your DS will need an (up-to-date) assessment of his needs. DD ended up having two needs assessments. One assessing her actual special need; the other for assessing how much, and the nature of, support.
You will need a formal diagnosis. Transfer to uni, and support, will be easier if your son already has his assessment and additional needs set out. That said uni might do their own anyway if yours is not by an appropriate (authorised) body/psychologist. DD's assessment of needs was out-of-date by the time she got to uni and we had to pay for another one. The payback in support though is worth it ten-fold! DD has found special needs support at university to be fantastic.